This invention generally relates to water jet apparatus for propelling boats and other watercraft. In particular, the invention relates to mechanisms for shifting a water jet apparatus to selectively propel a craft in the forward or reverse direction.
It is known to provide a mechanism for reversing the direction of the water flow exiting the steering nozzle of a water jet propulsion system. The reverse gate is typically pivotable about a horizontal axis between up and down positions. In the up position, the reverse gate is clear of the water flow exiting the steering nozzle. In the down position, the reverse gate is disposed in the path of the exiting water flow. In its simplest embodiment, the reverse gate has a U-shaped channel which reverses the water flow exiting the steering nozzle.
It would be desirable if a boat operator could use the reverse gate as a brake when the boat is moving forward and needs to be stopped quickly. However, in order to accomplish this, what is needed is a reverse gate which can be deployed and retracted quickly.
The present invention is directed to a non-steerable reverse gate having a structure which is optimized for use in braking a forward-moving boat or other watercraft. In particular, this reverse gate is designed for quick deployment/retraction. The latter characteristic is critical to reverse function as a brake. The reverse gate is also designed so that the steering response in reverse is the same as an outboard or inboard/outboard. In effect, the transom thrusts to the side that the steering wheel is turned to.
In accordance with one preferred embodiment of the invention, the reverse gate comprises a pair of flow-reversing passages for providing reverse thrust when the reverse gate is deployed, a lateral steering passage for directing flow, discharged to one side by the steering nozzle, to the opposite side, and a central deflector body. The flow-reversing passages start on opposite sides of the deflector body and curve outward and forward. The lateral steering passage is located aft of the deflector body and reversing passages and has discharge openings on opposite ends thereof, i.e., on the port and starboard sides of the reverse gate. The center of the aft wall of the reversing passages has an aperture, which allows water discharged from the steering nozzle to enter the steering passages. The deflector is situated in front of the aperture to deflect the pump discharge to the sides. The deflector in accordance with the preferred embodiments takes the form of a flat body having an oval cross section with rounded side edges and having an hourglass shape when viewed from front or rear. The front surface of the flat body is preferably either laterally and vertically straight or laterally straight and vertically curved.
The front surface of the deflector body directly opposes the steering nozzle outlet when the latter is in its central position. A reverse gate having the above-described structure functions to some degree as a pressure vessel with four discharge ports. When the steering nozzle is centered, the primary water exit path is spray which bounces off of the deflector and flows forward through the reversing passages. Steering, i.e., turning the steering nozzle about its pivot axis, allows some of the nozzle discharge to miss the deflector and escape around the backside, through the aperture behind the deflector body and into the steering passages. The flow around the deflector is facilitated by the Coanda effect.
Preferably, the deflector has a vertical rib on the centerline to split the nozzle discharge. This has the effect of obstructing the flow from transitioning to steering thrust too suddenly.
In accordance with the first preferred embodiment, the discharge xe2x80x9csplayxe2x80x9d angle at the reversing passage outlet was approximately 10 degrees per side. This angle optimized reverse thrust as well as reducing the counteracting steering thrust. However, other angles can be used. Preferably the discharge angle of the reversing passages in the preferred embodiments is selected to reduce opposing steering thrust.
The first preferred embodiment further comprises a pair of baffles located in the reversing passages adjacent to the steering nozzle. These baffles enhance steering thrust by directing more water around the deflector when the steering nozzle is turned.
In accordance with a second preferred embodiment, the deflector body has a concave front surface which is curved vertically and straight laterally, forming a simple curve. Preferably, the simple curve is an arc centered at the gate pivot centerline, to reduce opening and closing loads. This deflector improves steering thrust significantly. Also, the surfaces of the reverse housing immediately adjacent to the steering aperture are curved vertically and straight laterally, forming a simple curve. This structural feature straightens the flow and defines the discharge angle. The steering thrust creates a venturi effect, which scavenges the opposite side of the steering passage and perhaps the forward section of the reverse gate. Other structural features of the second preferred embodiment are similar to those of the first preferred embodiment.